#include <stdio.h>
#include <math.h>

#define PI 3.141592653589793

double square(double x) {
    return x * x;
}

int main() {
    double x1, y1, x2, y2, x3, y3;
    double a2, b2, c2;
    double r;
    while (~scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3)) {
        a2 = square(x1 - x2) + square(y1 - y2);
        b2 = square(x1 - x3) + square(y1 - y3);
        c2 = square(x3 - x2) + square(y3 - y2);
        r = sqrt(c2 / (1 - square(a2 + b2 - c2) / a2 / b2 / 4)) / 2;
        printf("%.2lf\n", 2 * PI * r);
    }
    return 0;
}